1. Field of the Invention
The invention relates to a canister for an evaporated fuel treatment apparatus which collects a fuel evaporated, for example, from a fuel tank in an internal combustion engine and discharges the collected fuel to an intake system.
2. Description of the Related Art
There is disclosed in U.S. Pat. No. 4,658,796 an evaporated fuel treatment apparatus structured such that only a vapor phase fuel can be introduced to an adsorbent in a canister by arranging a liquid trap for separating a gasoline vapor into a vapor phase and a liquid phase on a passage extending from a tank port communicated with a fuel tank to the adsorbent, thereby preventing the adsorbent from deteriorating due to an attachment of a component having a high boiling point of the liquid phase fuel to the adsorbent.
The apparatus is structured, as shown in FIG. 9, such that a second partition wall 20 having both ends extending to a casing 11 is arranged between an opening portion of a tank port 13, mounted on the casing of a canister 2, into the casing and a first diffusion chamber 12 on an inlet side of the canister so as to form a liquid trap 21, and the tank port 13 is opened between the liquid trap 21 and the casing 11. A first passage 22 for communicating the liquid trap 21 with the first diffusion chamber 12 is provided in the second partition wall 20. A fuel in a liquid phase flowing into the canister at a time of a sudden turn of a vehicle is supplied to the liquid trap 21, and only the fuel in a vapor phase flows into the first diffusion chamber 12 via the first passage 22 and is diffused at the first diffusion chamber so as to collect the fuel with the adsorbent 10.
Further, with respect to the fuel in a liquid phase collected in a lower portion within the liquid trap 21, air out of the canister 2 rises in temperature to evaporate the liquid phase fuel and the adsorbent 10 adsorbs the fuel via the first passage 22.
The fuel in a vapor phase flows into a third diffusion chamber 15 from a carburetor float chamber (not shown) after passing through a passage opening/closing valve which is opened when an engine is stopped and further passing through an outer bent port 19 of the canister 2, and is diffused so as to collect the fuel with the adsorbent 10.
A second diffusion chamber 14 on an outlet side of the canister 2 is provided between the adsorbent 10 and a lower end of the casing 11, and is communicated with the atmosphere by a first atmosphere port 18 provided in the casing 11.
A purge port 17 communicated with an intake passage (not shown) is open to the first diffusion chamber 12 on the inlet side of the canister separated from a third diffusion chamber 15 by a first partition wall 16 having an end buried in the adsorbent 10.
In accordance with the conventional technique mentioned above, since a position of a lowermost end of the tank port 13 and a position of an upper end of the first passage 22 communicated with the first diffusion chamber 12 receiving the adsorbent 10 therein are close to each other, a distance between the both is short and diameters of the tank port 13 and the first passage 22 are substantially the same, it is hard that the fuel in a vapor phase is liquefied in the liquid trap 21, so that the fuel in a vapor phase enters into the first diffusion chamber 12 from the first passage 22 without changing it to the liquid phase so as to be adsorbed to an activated carbon 10 as the adsorbent. Accordingly, there has been a problem that a performance of the activated carbon is deteriorated. Further, since the position of the lower end of the tank port 13 is disposed above the liquid trap 21, there is a little effect that the fuel in a liquid phase flows backward due to a negative pressure within the tank when the fuel tank is cooled, so that the fuel in a liquid phase is easily collected in the liquid trap 21. When a lot of fuel in a liquid phase is collected in the liquid trap 21, the fuel in the vapor phase enters into the first diffusion chamber 12 from the first passage 22 without being separated into the vapor phase and the liquid phase so as to be adsorbed to the activated carbon 10. Accordingly, in this view, there has been a problem that a performance of the activated carbon is deteriorated.
An object of the present invention is to provide a canister for an evaporated fuel treatment apparatus which can solve the problems mentioned above.
In order to solve the object mentioned above, in accordance with the present invention, there is provided a canister for an evaporated fuel treatment apparatus comprising a liquid trap for separating a gasoline vapor generated from the tank into the vapor phase and the liquid phase, wherein a tank port connected to the tank is arranged in a lower end portion of the liquid trap, an opening portion of a canister communication passage communicated with a diffusion chamber having an adsorbent is arranged in an upper portion within the liquid trap, and an inner diameter of the canister communication passage is set to be smaller than an inner diameter of the tank port.
In general, when the fuel tank is not cooled and the evaporated fuel is rich, the fuel in a vapor phase in a pipe between the tank and the canister is pressurized in a direction of the canister due to a pressure of evaporation. Then, the fuel in a vapor phase introduced into the liquid trap is cooled so as to become a liquid phase. In accordance with this structure of the present invention, a fuel in a liquid phase corresponding to a difference between the position of the lower end of the tank port and the position of the opening portion of the canister communication passage can be collected in the liquid trap. Further, when the fuel tank is cooled and the inner portion of the tank is in a negative pressure state, the fuel in a liquid phase within the liquid trap flows backward, so that the fuel in a liquid phase is not continuously collected within the separation chamber.
Further, since the inner diameter of the canister communication passage is smaller than the inner diameter of the tank port, the pressure of the fuel in a vapor phase increases within the liquid trap so as to be easily liquefied. As a result, an amount of the fuel in a vapor phase adsorbed to the adsorbent is reduced, so that a life of the adsorbent is extended.